1. Field of the Invention
The present invention relates to a boundary apparatus for controlling the connection between communication networks and, more particularly, to a boundary apparatus for mapping a resource reservation protocol (e.g., RSVP) in an ATM network for the purpose of controlling the quality of communication in an IP network (Internet Protocol Network) in the network structure in which the ATM network exists between a transmitting terminal in an IP network and a receiving terminal in another IP network, and the method of controlling the connection by the boundary apparatus.
2. Description of the Related Art
Recently, internets have been rapidly developing owing to the improvement and expansion of applications. Especially, owing to the image and sound superposing technique and the hyperlinkage technique which have been realized in a www (world wide web), internets have been developing as a communication means which becomes more accessible and which gives a feeling that the correspondents are actually conversing face to face. On the other hand, the problem of delay in communication in a network has become remarkable. One reason is that an appropriate means or technique does not catch up with the increase in the traffic, but the root cause is that internets are based on the best-effort transfer system which transfers IP packets with the best effort.
In the transfer circumstance of the best-effort system, the best efforts are directed only on transferring the packet which has arrived to the next stage without discriminating the packet by the user or the application, and the packets which can not be transferred, for example, the packets which overflow the buffer are discarded as they are. The discarded packets are detected at the end terminal by a TCP (Transmission Control Protocol) which is upper on the IP layer, and retransmitted, thereby avoiding discard. The retransmission, however, leads to some evils. For example, unnecessary packets stay in the network, and the prevention of a delay in the transfer is not guaranteed to a real-time application.
In order to eliminate these problems, the method of realizing the QoS (Quality of Service) has been investigated by the IETF (Internet Engineering Task Force), and the QoS control technique in the IP layer based on the RSVP (Resource Reservation Protocol) version 1 was already standardized and the study has been continued toward the realization thereof.
An RSVP is a control protocol for resource reservation in an IP layer, and exerts the control shown in FIG. 62. In this control, control messages (Path message, Reserve message) are transmitted and received between a router 2 which supports an RSVP on IP network 1 and a sender 3 of information (transmitting terminal), and between the router 2 and a receiver 4 (receiving terminal). Due to the control, memory resource and the like within the transmission path and the router 2 are reserved for the application of the sender 3, and the quality of communication is guaranteed. Generally, the sender 3 is able to provide the same information for a plurality of receivers 4 by point-multipoint communication (multicast).
The sender 3 first transmits a Path message containing traffic characteristics of the contents which are delivered to the receivers 4. The Path message is transferred along the routers 2 and distributed into a plurality of receivers 4. Each of the receivers 4 returns a Reserve message containing the resource which requires reservation to the sender 3 by reference to the contents of the Path message. The router 2 on the way merges the requests for reservation sent from the plurality of receivers 4 and transfers the Reserve message to the router 2 on the upper stream and the sender 3, and reserves the transmission path (bandwidth) and the memory resource for the receivers 4.
The mechanism of bandwidth reservation by the RSVP will be schematically described in the following. This mechanism is based on RFC2205 (Resource Reservation Protocol (RSVP)-Version 1 Functional Specification).
In the RSVP, the data flow to a specified destination and a transport layer protocol is defined as a session. The destination of a certain session (data flow) is generally defined by DestAddress. The DestAddress corresponds to the IP destination address which is written on the IP header potion of an IP packet. The process of bandwidth reservation consists of the following steps 1 to 4. It is here assumed that all of the transmitting terminal (sender host), the receiving terminals (receiver host) and the nodes (routers) on the path mount the RSVP.
(1) Establishment of Session
A route is set between the transmitting terminal and each of the receiving terminals by a certain routing protocol. The receiving terminals join a multicast group which is determined by the DestAddress according to an IGMP (Internet Group Multicast Protocol) or the like.
(2) Transmission of a Path Message
The transmitting terminal periodically transmits a Path message to the route (i.e., each DestAddress) established by the routing protocol. The Path message contains information on the data transmitted from the transmitting terminal, for example, IP address, traffic characteristics, and the IP address of the previous Hop to the transmitting terminal, as will be described later in detail.
Each node on the path holds the information on the transmitting terminal and the session as a Path state on the basis of the information in the Path message, and when the node receives a new Path message, it updates the Path state in accordance with the contents thereof and transfers the updated Path state to the next Hop (node). Similar operations are repeated thereafter, and the Path message ultimately reaches all the receiving terminals.
(3) Transmission of a Reserve Message
Each receiving terminal transmits a message for resource reservation (Reserve message) to the transmitting terminal. The Reserve message is transmitted to the Previous IP address (the IP address of the HOP on the upper stream) which is held in the Path state of each node. As will be described later, the Reserve message contains the QoS information which is required by the receiving terminal, the information on the form of bandwidth reservation, the IP address of the node to which the Reserve message is transmitted (i.e., the previous IP address), etc.
(4) Processing by Each Node which has Received a Reserve Message
The RSVP controller of each node which has received Reserve message reserves a bandwidth. The RSVP controller holds the reservation information as a reservation state on the basis of the QoS information, the information on the form of bandwidth reservation, etc. required in the message. The RSVP controller also merges the reservation state from each route, and holds the merged information for finally reserving the bandwidth as a traffic control state.
The RSVP controller requires the traffic controller of the node to reserve the bandwidth on the basis of the traffic control state information. The admission control section of the traffic controller judges whether or not the required QoS is to be accepted. That is, whether or not the required QoS is to be accepted is determined in accordance with whether or not a bandwidth corresponding to the required QoS is vacant. If the acceptance is possible, the admission control section secures the bandwidth in accordance with the contents of the required reservation, and the RSVP controller transmits the Reserve message to the node of the previous IP address which is recorded in the Path state of its own node. On the other hand, if the acceptance is impossible, the RSVP controller discards the Reserve message and transmits an error message to the receiving terminal which has transmitted the Reserve message.
(c-1) Path message
FIG. 63 is an explanatory view of the format of a Path message.
The Path message PATH contains parameters which are necessary at least for supporting both GS (Guaranteed Service) and CLS (Controlled Load Service). An RSVP common header 4b is attached to an IP header 4a, and parameter fields 4c to 4h are attached to the RSVP common header 4b. A session field 4c which identifies the QoS session contains a destination address, protocol ID (which is freely determined by the sender) and a destination port (UDP service port of the destination). In the case of multicast, the multicast addresses is written in the destination address. In an RSVP HOP field 4d, the address of the previous RSVP router is written. This information designates the router to which the RESV message generated by the receiver is transferred. A TIME VALUE field 4e shows the effective period of the Path message. The value is freely determined by each network element, and the default value is 30 seconds. A SENDER TEMPLATE field 4f shows the address of the sender of the data. A sender TSPEC field 4g for showing the characteristics of data flow and an ADSPEC field 4h follow the SENDER TEMPLATE field 4f. The TSPEC contains information such as the peak bandwidth, the average bandwidth and the recommended bandwidth. The ADSPEC field 4h is provided with a field for a common portion and fields for respective specific services. In the field for common portion, path information necessary for each service is written, and the GS field contains parameters C, D necessary for the calculation of the largest delay. Nothing is substantially written in the field for CLS.
(C-2) Resource Reservation (RESV) Message
FIG. 64 is an explanatory view of the format of a resource reservation message.
The format of the Reserve message RESV is common to that of the Path message PATH as far as the IP header field 5a, the RSVP common header field 5b, the session field 5c, the RSVP HOP field and the TIME VALUE field 5e. A STYLE CLASS field 5f follows the TIME VALUE field 5e. In the STYLE CLASS field 5f, the style WF/FF/SE of reservation of RSVP is written. A FLOW SPEC field 5g consists of TSPEC and RSPEC. The traffic characteristics (required bandwidth, etc.) required by the receiver are written in the TSPEC. The TSPEC holds the same value as or a lower value than the value of the TSPEC contained in the Path message. In the GS field, the receiver requires the bandwidth by the RSPEC (combinations of parameters R and S). The resource reservation at each router is executed in accordance with the TSPEC and the RSPEC. The destination of the RESV message is written in the FILTER SPEC field 5h. 
As a communication network having a different form from that of the IP network which executes the above-described communication quality control, there is an asynchronous transfer mode (ATM) network. The ATM is a transfer technique which is specified by ITU-T (International Telecommunication Union-Telecommunication Standardization Sector), etc. as a solution of a future ISDN (Integrated Services Digital Network).
The ATM originally aimed at realizing effective transfer and economical networking irrespective of the kind of media by uniformly dealing with and transferring any service as the cells of a short fixed length (53 bytes). Thereafter, the ATM has been applied to ATM-LAN and the like by utilizing the strong QoS control technique, and it is now in a process of application to a service of a higher real-time quality such as image transfer.
The ATM is basically adopted by the communication of connection type. Communication is executed after a virtual connection is established in advance in a network consisting of terminals and an ATM switches using a VP (Virtual Path) or a VC (Virtual Channel). A VP/VC is identified by a virtual path identifier VPI/a virtual channel identifier VCI which are written in the header portion of an ATM cell. These identifiers are also called ATM connection identifiers. The process of establishing a VP/VC is into two types. One is a PVP/PVC (Permanent VP/Permanent VC) process for establishing semipermanently a VP/VC by an operation system OPS or the like. The other is an SVP/SVC (Switched VP/Switched VC) process for establishing a VP/VC by a signaling process when an application is necessary. In establishing a VP/VC, the user reports the bandwidth and the quality class which are necessary for communication, and secures the VP/VC.
In the SVP/SVC process, the call setting and the call releasing are executed by transmitting and receiving signaling messages (Setup message, Release message, etc.) which are defined by the ITU-T Q.2900 series. FIG. 65 shows the process of establishing such a connection. In FIG. 65, ATM switches 12 are provided in the ATM network 11, and data are transferred between a transmitting terminal 13 and a receiving terminal 14.
When a call is set, a Setup message is transmitted from the transmitting terminal 13, and negotiation is executed between the transmitting terminal 13 and the ATM switch 12, and between the ATM switch 12 and the receiving terminal 14. When the Connect message transmitted from the receiving terminal 14 reaches the transmitting terminal 13, a channel (connection) for user data is established.
In the ATM, it is possible to distribute a message from one sender (Root) to a plurality of receivers (Leaves) by a point-multipoint call setting process (multicast setting process), as shown in FIG. 66. In this case, the sender 15 first transmits a Setup message (SETUP#1, SETUP#2) to a first receiver 18 via a switch 16, and a connection is established between the sender 15 and the receiver 18. Thereafter, a next receiver 19 is added by an ADD party message ADD PARTY.
When the switch 16 receives ADD PARTY from the sender 15, it transmits a Setup message (SETUP#3, SETUP#4) to a receiver 19 via a switch 17. When the switch 16 receives a Connect message CONNECT from the receiver 19, it returns an ADD Party Ack. message to the sender 15. In this manner, the receiver 19 is added to the connection which has been established between the sender 15 and the receiver 18 as a party.
Similarly, when the sender 15 transmits an ADD party message, a third receiver 20 is added to the connection. It is possible to add a fourth and subsequent receivers in a similar process. Additionally, in an ATM forum, the process for establishing a point-multipoint call led by a receiver is also defined.
Transfer of IP packets in the ATM has already been frequently executed in a WAN (Wide Area Network) and the like. However, transfer in such a network is best-effort transfer by a point-point connection, and the quality securing control by the RSVP is limited to an IP layer.
It is considered that the use of the resource securing mechanism controlled by the RSVP in combination with the connection control mechanism utilizing the quality control and the point-multipoint control in the ATM enables more flexible and more reliable communication having a higher network usage ratio than IP communication. The technique of combination, however, has not been established.
The IETF is at present standardizing Integrated Service so as to realize QoS securing service. Only the RSVP is proposed as the signaling protocol for such a service, but the technique of mapping an RSVP in an ATM network has not been established, as described above.
The resource reservation process by an RSVP is started by a resource reservation message (Reserve message) from a receiving terminal, as described above. On the boundary between an ATM network and an IP network, a boundary apparatus (IP-ATM combining apparatus) which has both the functions of IP communication and ATM communication is provided. Accordingly, in order to map the RSVP in the ATM network, it is only necessary to establish an ATM connection such that when the boundary apparatus receives the Reserve message, the quality required by the RSVP may be guaranteed.
FIG. 67 shows the structure of a communication network containing such a boundary apparatus. This network is composed of IP networks 31, 32-1 to 32-n, and an ATM network 33 provided between those IP networks. It is assumed here that data is transferred by point-multipoint transfer between a transmitting terminal S in the IP network 31 and each of the n receiving terminals R1 to Rn in the respective IP networks 32-1 to 32-n via the ATM network 33.
The ATM network 33 contains an ATM switch ATMsw, and a boundary apparatus EN0 is provided on the boundary between the IP network 31 of the transmitting terminal S and the ATM network 33, while boundary apparatuses EN1 to ENn are provided on the respective boundaries between the IP networks 32-1 to 32-n of the receiving terminals R1 to Rn and the ATM network 33. The ATM network 33 generally contains a plurality of ATM switches, but only one is shown in FIG. 67 for convenience of explanation. The structure and the operation of the following example is the same even if a plurality of ATM switches are provided.
If an ATM network exists on the route from the transmitting terminal to the receiving terminal, as described above, high-quality communication is enabled by an ATM quality control mechanism which directly establishes an ATM connection between the boundary apparatuses, converts IP packet data into ATM cells, and transfers the cells through the ATM connection.
FIGS. 68 and 69 are explanatory views of a control process in IP communication via an ATM network. The symbol S denotes a sender, RT1-RT2 routers, Sw an ATM switch, and R a receiver. It is assumed that the route between the sender S and the receiver R has been obtained by a routing protocol.
The sender S first transmits a PATH message toward the receiver R. The PATH message arrives the receiver R via the router RT1, the boundary apparatus EN0 on the transmission side, the boundary apparatus EN1 on the reception side and the router RT2. When the receiver R receives the PATH message and wants to receive the data from the sender S, the receiver R writes the bandwidth (required bandwidth) necessary for the reception of the data in the RESV message and transmits the RESV message in the opposite direction to the direction of the PATH message. The RESV message reaches the boundary apparatus EN0 on the transmission side via the router RT2 and the boundary apparatus EN1 on the reception side. When the RESV message arrives, the boundary apparatus EN0 on the transmission side judges whether or not it is possible to secure the required bandwidth, and if it is possible to secure the required bandwidth, the boundary apparatus EN0 transfers the SETUP message to the boundary apparatus EN1 on the reception side by using an ATM signaling message. If the boundary apparatus EN1 on the reception side is able to establish a connection, it returns a CONNECT message to the boundary apparatus EN0 on the transmission side in response to the SETUP message. As a result, an ATM connection for data transfer is established. When the boundary apparatus EN0 on the transmission side receives the CONNECT message, it transfers the RESV message received from the receiver R to the sender S.
In FIG. 70, the physical structure of the network is divided into an IP layer and an ATM layer. In the IP layer, the transmitting terminal S executes IP communication to the receiving terminals R1 to Rn via the boundary apparatuses EN0, EN1 to ENn, and the in the ATM layer, the boundary apparatus EN0 on the transmission side establishes an ATM connection between the boundary apparatus EN0 and each of the boundary apparatuses EN1 to ENn on the reception side, and executes ATM communication. The transmitting terminal S and the receiving terminals R1 to Rn have a function of transferring a packet by an IP protocol, and each of the receiving terminals R1 to Rn has its own IP address. For example, when the transmitting terminal S transfers application data to the receiving terminals R 1 to Rn, the data are divided into packets (datagrams) of a variable length by an IP processor, and after IP addresses of the destinations are added thereto, the packets are transmitted to the transmission paths. The receiving terminals R1 to Rn assemble the received packets into the original data and transfer the data to an application executing portion.
The ATM switch is placed in the ATM network 33, and data are divided into cells for switching. All the data which transfer into the ATM network 33 are divided into cells of 53 bytes.
The boundary apparatuses EN0, EN1, to ENn between different networks (IP network and ATM network) have both a function of dividing the IP packets which have arrived from the IP networks 31, 32-1 to 32-n into ATM cells and transferring the cells to ATM network 33, and the opposite function thereof. In addition, the boundary apparatuses EN0, EN1 to ENn have a function of deciding the route of IP packets as an IP communication function, and a function of switching ATM cells and establishing an ATM connection as an ATM communication function.
The boundary apparatuses EN0, EN1 to ENn further have the following three functions.
(1) Bandwidth Control Function
This function includes a policing function for deciding what kind of ATM connection is to be established in which bandwidth on the basis of the bandwidth required by the receiving terminals R1 to Rn.
(2) Connection Control Function
The boundary apparatuses control the remaining unused VPI/VCIs and the vacant bandwidth, judges whether or not it is possible to offer the VPI/VCIs and the required bandwidth when a new bandwidth is required (admission control), and executes signaling.
(3) Address Resolution Connection
When an IP packet is transferred to the target receiver via the ATM network 33, it is necessary to obtain the ATM address (VPI/VCI) of the destination selected from the boundary apparatuses EN1 to ENn using the flow identifier (session identifier). As the flow identifier, the IP address of the destination is used. Each boundary apparatus (1) holds a routing table so that the IP address of the boundary apparatus to which the receiving terminal as the destination is connected can be obtained from the IP address of the receiving terminal, and (2) holds the IP address-ATM address (VPI/VCI) conversion table (address resolution table).
As described above, the control messages of the RSVP are transmitted from both the transmitting terminal S and a receiving terminal Ri. In order to transfer these control messages via the ATM network 33, an ATM connection is directly established between the boundary apparatus EN0 on the transmission side and each of the boundary apparatus EN1 to ENn on the reception side which are placed on the boundary of the ATM network 33. By establishing the ATM connection, it is possible td prevent a delay in the processing time due to IP routing and to provide a high-quality connection for a control message. The connection for a control message is established separately from a connection for data transfer and is used for exclusively for the transfer of a control message.
There are two methods of establishing an ATM connection for a control message, as shown in FIGS. 71 and 72. FIG. 71 shows a method of establishing an ATM point-point connection in two ways between the boundary apparatus EN0 on the transmission side and each of the boundary apparatus EN1 to ENn on the reception side. In this manner, it is possible to provide a high-quality path for transferring a control message in two ways for each of the boundary apparatus EN1 to ENn on the reception side.
FIG. 72 shows a method of using an ATM point-multipoint connection in combination with an ATM point-point connection. In this method, with respect to downward communication from the transmission side to the reception side, a point-multipoint connection is established between the boundary apparatus EN0 on the transmission side and the boundary apparatuses EN1 to ENn on the reception side, while, with respect to upward communication, ATM point-point connections are individually established for the respective boundary apparatus EN1 to EN0 on the reception side. By using the ATM point-multipoint connection for downward communication, it is possible to effectively utilize the VPI/VCI resource and the bandwidth resource between the boundary apparatus EN0 and the ATM switch.
As described above, in order to transfer the control message of a communication quality control protocol which is operated in the IP network, an ATM point-point connection or an ATM point-multipoint connection is used in the ATM network 33.
As a transfer method using an established connection, a best-effort transfer or a transfer with a QoS guarantee will be considered. In a signaling protocol such as an RSVP which holds a state by a software state, a loss of a control message packet directly leads to a deterioration in the efficiency of the protocol. For this reason, it is desirable to prepare a transfer route with some QoS guarantee for a connection for transferring a control message.
One of the problems of an ATM mapping technique which maps an RSVP in an ATM network is what kind of connection of which bandwidth is allocated to a request for resource (bandwidth) generated from each of a plurality of users (receivers).
The bandwidth BWr(i) required by the receiving terminal Ri (i=1, 2 . . . ) is different from another bandwidth required by another receiving terminal. However, if the ATM switch sets a different SVC for each of the receiving terminals, SVC resource will be exhausted (VPI/VCIs will be wasted).
An RSVP is a protocol which is defined on the assumption of multicast to a plurality of receiving terminals R1 to Rn, and a plurality of receivers require different resources (bandwidth). An ATM technique includes a point-multipoint (p-mp) connection for one to multi communication which supports multicast. In an ATM network, however, one p-mp connection can only be established in one bandwidth. This causes another problem. More specifically, if a plurality of receivers require connections in different bandwidths such as in the RSVP, it is necessary to establish a p-mp connection in the largest bandwidth of all the required bandwidths in order to satisfy the requests from all the receivers. That is, it is necessary to establish a multiconnection in the largest bandwidth for each receiver, which leads to the waste of a network resource.
In addition, when an RSVP is used, the bandwidth BWs recommended by a transmitting terminal and the bandwidth BWr required by a receiving terminal changes with time. If an SVC is reset in the ATM network with every change, there is a fear of an overload of the processor in the ATM switch.
FIG. 73 is an explanatory view of the establishment of a p-mp connection between the boundary apparatus EN0 on the transmission side and five boundary apparatus EN1 to EN5 on the reception side.
With respect to one multicast session offered from a sender, there are bandwidths required by five receivers which belong to the boundary apparatuses EN1 to EN5. The required bandwidths are different from each other. If it is assumed that the unit of the optional bandwidth is B, the boundary apparatuses EN1 to EN5 receive the requests for bandwidths 10B, 5B, 6B, 1B, and 2B from the respective receivers. Of all the five required bandwidths, the largest one is 10B. If the ATM network 33 services through only one p-mp connection, it is necessary to establish a connection of a bandwidth of 10B. According to this method, since only one connection suffices, it is possible to economize VPI/VCIs. However, since a bandwidth of 10B is provided for the receiver which requires a bandwidth of only 1B, the network resource (bandwidth resource) is wasted.
On the other hand, if the establishment of a connection faithful to the request from a receiver is considered. it is natural for the ATM network 33 to utilize a point-point (p-p) connection for one-to-one communication. If the ATM network 33 services to every receiver through a p-p connection, connections of bandwidths required by the respective receivers are established, as shown in FIG. 74. According to this method, since a connection of a bandwidth required by a receiver is established, there is no waste of a bandwidth in each connection itself. However, since it is necessary that the boundary apparatus EN0 on the transmission side provides the number of connections corresponding to the number of requirements, there is a waste of a VPI/VCI. In addition, since there are a plurality of connections with respect to one data transmitted in the same direction, there is a waste of bandwidth resource on the side of the ATM network of the boundary apparatus EN0 on the transmission side. This tendency increases toward the transmission side.
As described above, in the ATM network 33, it is difficult to establish a connection of an appropriate bandwidth with respect to a multicast session. In order to solve these problems, combined use of the two connection systems (p-mp connection and p-p connection) will be considered. That is, a method of supporting a multicast session by combining a p-p connection with a p-mp connection will be effective. In the prior art, however, no method has been provided for the optimum combination of a p-p connection and a p-mp connection.
Accordingly, it is an object of the present invention to eliminate the above-described problems in the related art and to avoid the exhaustion of the SVC resource (VPI/VCI resource) in an ATM network and reduce the number of times of setting an SVC even if the bandwidth BWs recommended by a transmitting terminal and the bandwidth BWr required by a receiving terminal changes.
It is another object of the present invention to enable the optimum combination of a point-point connection (p-p connection and a point-multipoint connection (p-mp connection) in an ATM network to be selected when an IP packet is transmitted to a plurality of receivers which require different bandwidths.
It is still another object to enable the optimum connection to be established with consideration for the resource (VPI/VCI resource and the bandwidth resource) usage state between the boundary apparatus on the transmission side in which the exhaustion of the tag resource (VPI/VCI) and the bandwidth resource is the largest and an ATM switch which is connected to the boundary apparatus.
It is a further object of the present invention to enable the optimum connection for data transfer service to be established in an ATM network with consideration for the effective bandwidth usage ratio of not only the bandwidth between the boundary apparatus on the transmission side and an ATM switch which is connected thereto but also the bandwidth used by another ATM switch in the ATM network, i.e., the effective bandwidth usage ratio of the entire ATM network.
It is a further object of the present invention to instruct the separation of an existent connection in a case where the separation of the existent connection increases the effective bandwidth allocation ratio in an ATM network.
It is a still further object of the present invention to suppress the separation or re-establishing of a connection in a state in which the number of reservation requests from receivers rapidly changes, for example, at the time of starting a data transmitting session and at the time of changing contents, thereby preventing an increase in the amount of signaling message in an ATM network and lightening the signaling processing load on not only a boundary apparatus but also each ATM switch.
It is a still further object of the present invention to instruct the separation or re-establishing of a connection when the effective bandwidth allocation rate increases by introducing the variance of required bandwidths, more specifically, the square variation coefficient of the required bandwidths.
It is a still further object of the present invention to separate one multicast connection into an existent connection and a new connection by a simple method so that the effective bandwidth allocation rate may increase, when the separation is necessary.
It is a still further object of the present invention to lighten the signaling processing load of an ATM switch by limiting the number of requests for resource belonging to a new connection after one multicast connection is separated into an existent connection and the new connection.
It is a still further object of the present invention to periodically monitor the effective bandwidth allocation ratio on the assumption that two adjacent connections are unified for each data transmission session, and to unify the connections while suppressing a drop of the effective bandwidth allocation ratio on the basis of the result of monitoring, so as to eliminate a shortage in the resource between the boundary apparatus on the transmission side and an ATM switch, and while introducing the variance of required bandwidths, more specifically, the square variation coefficient of the required bandwidths so that a high effective bandwidth allocation rate can be maintained in the unified connection.
It is a still further object of the present invention to lighten the signaling processing load on an ATM switch or the like by unifying connections such that the number of requests for resource belonging to the unified connection does not exceed a preset value.
To achieve these objects, in a first aspect of the present invention, there is provided a method of establishing a single p-mp connection in an IP communication network for executing one to N communication (1-to-N communication) between a transmitting terminal and a plurality of receiving terminals, the IP communication network having an ATM network between an IP network accommodating a transmitting terminal and an IP network accommodating N receiving terminals, boundary apparatuses having an IP communication function and an ATM communication function and provided on the boundaries between the respective IP networks and the ATM network, and the connection established in the ATM networks so as to execute 1 to N communication between the transmitting terminal and the plurality of receiving terminals.
(a-1) First Method
If it is assumed that the recommended bandwidth transmitted from a transmitting terminal to a receiving terminal in accordance with a communication quality control protocol with respect to one data transmission session is BWs, the boundary apparatus on the transmission side establishes a point-multipoint connection (p-mp connection) of a bandwidth of BWs/xcfx81(k) so as to execute 1 to N communication, wherein xcfx81(k) is the usage ratio of not more than 1.
(a-2) Second Method
If it is assumed that the largest required bandwidth of the bandwidths BWr(i) required by the respective receiving terminals with respect to one data transmission session is BWmax, the boundary apparatus on the transmission side establishes a point-multipoint connection (p-mp connection) of a bandwidth of BWmax/xcfx81(k) so as to execute 1 to N communication, wherein xcfx81(k) is the usage ratio of not more than 1.
In this manner, it is possible to avoid the exhaustion of the SVC resource (VPI/VCI resource) in the ATM network. In addition, since the bandwidth of the p-mp connection does not change or does not frequently change even if the bandwidth BWr required by a receiving terminal changes, it is possible to reduce the number of times of setting an SVC. Furthermore, since xcfx81(k) is set such as to become smaller as the number of connections accommodated in the link increases, in other words, since the bandwidth of the p-mp connection is established to be large, even if the number of connections accommodated in the link increases and the bandwidth allocation is unstable, the user can transmit data with a desired quality.
(Separation of a Connection)
In a second aspect of the present invention, there is provided a method of establishing a connection in an IP communication network having an ATM network between an IP network accommodating a transmitting terminal and an IP network accommodating N receiving terminals, boundary apparatuses having an IP communication function and an ATM communication function and provided on the boundaries between the respective IP networks and the ATM network, in which the receiving terminals require predetermined resources (bandwidths) with respect to one data transmission session in accordance with a communication quality control protocol, and the boundary apparatus on the transmission side establishes a point-multipoint connection or a point-point connection in the ATM network on the basis of the required bandwidth from each receiving terminal so as to execute 1 to N communication between the transmitting terminal and the N receiving terminals. The connection is established in the following manner.
(b-1) Judgment as to Separation
The requests for bandwidth from the receiving terminals are divided into a plurality of groups depending upon the required bandwidths, and one p-p connection or p-mp connection is established for each group. When the number of requests of bandwidth changes, if the effective bandwidth allocation ratio of the connection which corresponds to the group in which the number of requests for bandwidth changes is not more than a preset value, the requests belonging to the group is separated into two groups so as to improve the effective bandwidth allocation ratio, and a connection is established for each separated group. In this manner, it is possible to establish an optimum connection for data transmission with consideration for not only the bandwidth between the boundary apparatus on the transmission side and an ATM switch which is connected thereto but also the effective bandwidth usage ratio of the entire ATM network.
In addition, the preset value is made variable on the basis of the rate of change of the number of requests for bandwidth. In this manner, it is possible to suppress the separation or re-establishing of a connection in a state in which the number of reservation requests from receivers rapidly changes, for example, at the time of starting a data transmitting session and at the time of changing contents, thereby preventing an increase in the amount of signaling message in the ATM network and lightening the signaling processing load on not only the boundary apparatus but also each ATM switch.
Furthermore, whether or not the connection is to be separated is determined with consideration for the variance of the required bandwidths of the connection. In this manner, it is possible to separate or re-establish the connection so that the effective bandwidth allocation ratio may increase.
(b-2) Method of Separation
A plurality of bandwidth classes are set for each predetermined bandwidth, one group is composed of more than one class, and one connection is established for each group. When a connection is separated, the group corresponding to the connection (the group as the object of separation) is separated into two groups, and a connection is established for each of the separated groups. It is possible to divide the group in accordance with the following methods (1) to (3). In the first method (1), the group is divided into a group consisting of a predetermined number of classes of smaller bandwidths and a group of the rest, and one connection is established for each group. In the second method (2), the average value of all the required bandwidths belonging to the group as the object of separation is calculated, the group is separated into a group consisting of the smaller bandwidth classes, and a group consisting of the remaining classes on the basis of the average value, and a connection is established for each of the separated groups. In the third method (3), the number of requests is added up, beginning from the class of the minimum bandwidth in the group as the object of separation until the total sum reaches a preset value, the calculated classes form one group, and the rest the other group, and a connection is established for each of the separated groups.
If the methods (1), (2) of separation are adopted, it is possible to divide a group into two by a simple method and to improve the effective bandwidth allocation ratio. If the method (3) is adopted, it is possible to limit the number of requests for bandwidth which belong to the new connection, and to lighten the signaling processing load on the ATM switch.
In a third aspect of the present invention, there is provided a method of establishing a connection comprising the steps of classifying the requests for bandwidth into a plurality of groups on the basis of a required bandwidth, establishing a connection for each group, periodically calculating the effective bandwidth allocation ratio on the assumption that the two connections in adjacent bandwidths are unified, and unifying the connections of the two groups if the effective bandwidth allocation ratio is not less than a preset value, so as to establish one point-multipoint connection.
In this manner, it is possible to unify connections while suppressing a drop in the effective bandwidth allocation ratio, thereby eliminating a shortage in the resource between the boundary apparatus on the transmission side and the ATM switch. In addition, if the variance of the required bandwidths is introduced, it is possible to unify connections so that the high effective bandwidth allocation ratio may be maintained. If connections are unified under the condition that the number of requests in the unified connection is not more than a preset value, it is possible to lighten the signaling processing load on the ATM switch.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings.